Thanos Only Attacked Gamora's Planet to Defeat His Secret Nemesis

screenrant.com:

While Thanos' attack on Gamora's home planet of Zen-Whoberi was the darkest day of her life, the true horror of the situation was that it was just one of many attempts by the Mad Titan to weaken and defeat his secret nemesis, the being known as Magus. While Thanos' early years left him as a pirate king in charge of an army of brigands, his commitment to the cosmic embodiment of Death saw him quickly take on larger significance in the galaxy, earning him a class of enemy he wasn't yet able to defeat outright.

Thanos' attack on Zen-Whoberi wasn't based on blood lust, his love of Death, or even his MCU counterpart's desire for universal balance, but rather the desire to prevent Magus growing stronger. After massacring the pacifist population of the planet, Thanos «adopted» Gamora as her species' only survivor, raising her as the deadliest woman in the galaxy and unwittingly creating a hero who would stand against his schemes again and again. But while the significance of this event would shape her entire life,  Gamora's entire planet was wiped out as just one move in a cosmic chess match.

Related: Thanos' Original Infinity Stone Plan Proves the Gauntlet is Essential

The Magus is a dark version of the heroic Adam Warlock who draws his staggering power from an organization known as the Universal Church of Truth — a galaxy-spanning religion which converts its adherents' belief into pure power. That power is transmitted to its leaders, allowing them to conquer more worlds and win even more converts. In 2019's Thanos #1-6, Ariel Olivetti and Tini Howard chart Thanos' discovery that Magus will one day be his greatest threat. Knowing his followers are not yet capable of defeating Magus' church, Thanos characteristically resolves